Support is requested, in part, for the fourth Gordon Research Conference on Mammalian DNA Repair in 1993 - a biannual conference which brings together a diverse group of scientists interested in the molecular and genetic regulation of DNA in mammalian cells and the biological consequences of incomplete and inaccurate repair. This topic is of particular importance in assessment of the risk associated with exposure to environmental mutagenic and carcinogenic hazards, and is also of much interest to many other disparate areas such as the variations among individuals of the efficacy of chemotherapeutic agents, theories of aging, evolutionary divergence of biochemical processes, and mapping and cloning human genes which modify response to exposures. The conference provides the opportunity for the interaction, in an informal setting, of a group of scientists who often do not find themselves at the same meeting. Discussions between the participants are likely to lead to an exchange of ideas, techniques, and approaches which will benefit many different research projects and areas. This meeting will include nine sessions covering a range of areas in which progress is being made rapidly and will feature talks by leaders in the fields aimed not only at scientists in the immediate area but those in related disciplines. The sessions will cover chromatin structure, repair, and gene transcription, construction and use of site-specific lesions, damage- inducible responses, regulation of response to ionizing radiation damage, human repair deficient disorders, transgenic animals, and repair in a range of vertebrates and plants. Support is requested towards the travel and conference fees for key participants from the U.S. and overseas, especially young investigators, who otherwise would be unable to attend. The need to support foreign participants, in part, is particularly important to preserve an international contribution which has been very valuable in past conferences, and because the field of DNA repair involves many major participants in European and Asian countries.